[PATCH 3/4] KVM: MMU: reduce the size of mmu_page_path

[Xiao Guangrong]

Currently only PT64_ROOT_LEVEL - 1 levels are used, one additional entry
in .parent[] is used as a sentinel, the additional entry in .idx[] is
purely wasted

This patch reduces its size and sets the sentinel on the upper level of
the place where we start from

Signed-off-by: Xiao Guangrong <guangrong.x...@linux.intel.com>
---
 arch/x86/kvm/mmu.c | 32 ++++++++++++--------------------
 1 file changed, 12 insertions(+), 20 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index e273144..c396e8b 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -1984,12 +1984,12 @@ static bool kvm_sync_pages(struct kvm_vcpu *vcpu, gfn_t 
gfn,
 }
 
 struct mmu_page_path {
-       struct kvm_mmu_page *parent[PT64_ROOT_LEVEL];
-       unsigned int idx[PT64_ROOT_LEVEL];
+       struct kvm_mmu_page *parent[PT64_ROOT_LEVEL - 1];
+       unsigned int idx[PT64_ROOT_LEVEL - 1];
 };
 
 #define for_each_sp(pvec, sp, parents, i)                      \
-               for (i = mmu_pages_first(&pvec, &parents);      \
+               for (i =  mmu_pages_next(&pvec, &parents, -1);  \
                        i < pvec.nr && ({ sp = pvec.page[i].sp; 1;});   \
                        i = mmu_pages_next(&pvec, &parents, i))
 
@@ -2016,25 +2016,15 @@ static int mmu_pages_next(struct kvm_mmu_pages *pvec,
        return n;
 }
 
-static int mmu_pages_first(struct kvm_mmu_pages *pvec,
-                          struct mmu_page_path *parents)
+static void
+mmu_pages_init(struct mmu_page_path *parents, struct kvm_mmu_page *parent)
 {
-       struct kvm_mmu_page *sp;
-       int level;
-
-       if (pvec->nr == 0)
-               return 0;
-
-       sp = pvec->page[0].sp;
-       level = sp->role.level;
-       WARN_ON(level == PT_PAGE_TABLE_LEVEL);
-
        /*
-        * Also set up a sentinel. Further entries in pvec are all
-        * children of sp, so this element is never overwritten.
+        * set up a sentinel. Further entries in pvec are all children of
+        * sp, so this element is never overwritten.
         */
-       parents->parent[level - 1] = NULL;
-       return mmu_pages_next(pvec, parents, -1);
+       if (parent->role.level < PT64_ROOT_LEVEL)
+               parents->parent[parent->role.level - 1] = NULL;
 }
 
 static void mmu_pages_clear_parents(struct mmu_page_path *parents)
@@ -2051,7 +2041,7 @@ static void mmu_pages_clear_parents(struct mmu_page_path 
*parents)
                WARN_ON(idx == INVALID_INDEX);
                clear_unsync_child_bit(sp, idx);
                level++;
-       } while (!sp->unsync_children);
+       } while (!sp->unsync_children && (level < PT64_ROOT_LEVEL - 1));
 }
 
 static void mmu_sync_children(struct kvm_vcpu *vcpu,
@@ -2064,6 +2054,7 @@ static void mmu_sync_children(struct kvm_vcpu *vcpu,
        LIST_HEAD(invalid_list);
        bool flush = false;
 
+       mmu_pages_init(&parents, parent);
        while (mmu_unsync_walk(parent, &pages)) {
                bool protected = false;
 
@@ -2335,6 +2326,7 @@ static int mmu_zap_unsync_children(struct kvm *kvm,
        if (parent->role.level == PT_PAGE_TABLE_LEVEL)
                return 0;
 
+       mmu_pages_init(&parents, parent);
        while (mmu_unsync_walk(parent, &pages)) {
                struct kvm_mmu_page *sp;
 
-- 
1.8.3.1